Many residential and commercial developments have a retention pond. While this may add to the natural appeal of the landscape, a retention pond’s primary function is to manage water from roads, driveways and other impermeable surfaces. Runoff can often carry pollutants such as petroleum and heavy metals, such as copper and zinc.

Nutrients are also a concern, in particular nitrogen and phosphorus.

Excess nutrients cause algal blooms; and nothing destroys a water feature and its ecological balance like a green slimy cesspool. When algae die, oxygen is depleted from the water, called eutrophication, which stresses fish and micro-organisms, in some cases killing them.

Algaecides and other additives can be used responsibly to control algae, but other approaches can reduce the dependence on such products. Plants are a terrific way to reduce the availability of excess nutrients that inevitably lead to algae blooms.

At Trident Technical College, we recently installed wetland carpet along one of the retention pond shorelines. This product consists of iris, hibiscus and water canna rooted in burlap that was placed just below the water’s edge. The plants have quickly established themselves and soon will reduce erosion and buffer runoff that carries excess nutrients. In addition, the flowering plants are a visual improvement over turf as well as increasing plant diversity for wildlife.

While the perimeter of retention ponds is often landscaped to naturalize the setting as well as filter out contaminants, very few things grow inside the pond besides algae. In addition to planting the shoreline, we’ve installed floating wetlands to increase plant activity and diversity.

Floating wetlands are artificial islands with roots that dangle in the water. Not only are wetland plants utilizing free nitrogen and phosphorus, leaving fewer nutrients for algae to grow, they are a wonderful addition to the pond’s beautification.

There is a variety of floating wetland products, but we’ve used a buoyant mat with holes for six-inch pots. Plants root through the bottom of the containers into the water. In the winter, we’ll be able to pull the island ashore and remove the dying plant material before it releases nutrients back into the water when decomposing. And in subsequent years, we can connect another mat to expand our floating wetland.

Once planted, the island was anchored to opposing shores for easy retrieval.

The roots also boost microbe populations. The microscopic organisms such as bacteria are major consumers of pollutants, whether it’s nutrients or heavy metals. They proliferate on the surface area of dangling roots and the artificial island. Microbes are also the base of the aquatic food chain. Multicell organisms feed on microbes, small fish feed on multicell organisms, and so on. The food chain flourishes.

Research has indicated that floating wetlands can remove up to 20 times the amount of nitrogen and 10 times the amount of phosphate from a retention pond.

A New Zealand study indicated floating islands removed a significant portion of copper and zinc, in some cases more than half, and improved water clarity.

While floating wetlands reduce water problems, they may not be the only solution. Occasional treatments may still be needed to control algae and clarify water.

Consult a pond management company for options. Regardless, additional plants can lessen the dependence on chemicals while expanding wildlife habitat and beautifying a pond.

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